(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to particular chemistries for negative photoresist.
(2) Description of the Prior Art
Integrated semiconductor devices comprise electronic circuits of sub-micron and deep sub-micron dimensions and are typically created in or on the surface of a silicon substrate. The creation of semiconductor devices is supported by sophisticated and interacting, mutually supporting disciplines.
Device features are transposed from a mask onto a semiconductor surface using photolithographic imaging processes. Since this exposure depends on the transfer of photo energy from a source to a target surface, it is to be expected that, for target features that are created in very close proximity to each other, the transfer of photo energy interacts for very closely spaced device features, most commonly interconnect lines or contact holes having sub-micron spacing between adjacent lines.
A common measure for the occurrence of such interaction are applications where the Critical Dimensions (CD) of the layout of the Integrated Circuit (IC) approach the resolution limit of the lithography equipment. For such applications, proximity effects begin to influence the manner in which mask images are transferred to target surfaces. This interaction imposes limitations on the proximity of adjacent device features, these limitations are referred to as Critical Dimensions (CD) of a design and device layout.
Related application (TS01-376), filed on Nov. 30, 2001, Ser. No. 10/002,986, addresses problems and limitations that are encountered when creating openings on a semiconductor surface such as the surface of a layer of photoresist or the surface of a semiconductor substrate. This application provides two masks. The first mask, referred to as the packed mask, comprises the desired contact holes, which are part of the creation of a semiconductor device. To the packed mask are added padding holes in order to increase and condense the hole density of the packed mask. The second mask, referred to as the unpacking mask, comprises openings at the same locations as the locations of the padding holes of the first mask, the openings provided in the second mask have slightly larger dimensions than the padding holes of the first mask. A first exposure is made using the packed mask, a second exposure of the same surface area is made using the unpacking mask. The unpacking mask is used to selectively cover the padding contact holes, resulting in the final image. Two types of unpacking masks can be used, a first type having unpacking holes that surround the desired hole pattern, a second type having unpacking holes that align with the desired hole pattern.
Related application (TS01-463), filed on Dec. 5, 2001, Ser. No. 10/005,806 provides a method of creating contact holes using a packing and unpacking procedure, further applying a phase-shift mask. The Depth Of Focus (DOF) and Mask Error Factor (MEF) of closely packed holes can be improved using Alternating Phase Shifting Mask (Alt PSM) for the exposure of the holes. However, the Alt PSM is dependent on hole density or hole separation and is less effective where holes are relatively further separated from each other. In order to improve DOF and MEF performance for the creation of holes, the application adds extra holes to a given pattern of contact holes on the surface of a first mask, thus densifying the pattern of holes on the first mask and therefore reducing the range of the hole-diameter to hole separation ratio. The pattern of added holes is alternating in phase with the pattern of desired holes. The added holes will be filled up using a second mask.
U.S. Pat. No. 5,573,634 (Ham) shows a contact hole process using a double exposure photoresist process.
U.S. Pat. No. 5,308,741 (Kemp) shows a double exposure process with mask shifting and phase shifting.
U.S. Pat. No. 5,432,b44 (Shimizu) shows a double exposure process with a phase shift masks (PSM).
U.S. Pat. No. 5,017,461 (Abe), U.S. Pat. No. 5,998,092 (McCulloch et al.) U.S. Pat. No. 5,648,196 (Frechet et al.) and U.S. Pat. No. 5,532,113 (Frechet et al.) are related patents.